The present invention relates to the field of motor vehicle suspensions and, more particularly, to variable-stiffness suspensions.
This type of suspension is, specifically, increasingly widespread in response to needs of comfort of vehicles. The most frequently used solutions to obtain a variable stiffness consist in producing a spring suspension assembly in which the spring is a wire spring of variable section, the spring resting on an element made of elastomer: the stiffness is thus minimal while the smaller diameter coils of the spring are not in contact with the elastomer support element, then increases with the length of the coil in contact with the support element. In order to provide a good hold of the spring, the latter may be clipped to the elastomer support element; such a solution also allows a nonaggressive contact with the spring.
The production of a variable-section spring is however relatively costly, and other solutions have been envisaged for producing a variable stiffness of the assembly, in particular the use of a variable-flexibility support element which then makes it possible to use a wire spring of constant section (see for example, and in a nonexhaustive manner, document EP0924445).
A first embodiment of a variable-flexibility support element consists, for example, in forming a set of notches on the surface of the support element, made of an elastomer, in contact with the spring: at rest, the stiffness in compression is minimal; in the compression phase, the notches deform and the stiffness increases. This solution is however not entirely satisfactory: in particular, it has poor resistance to grit, the grit building up between the notches and being able to damage the spring. In addition, it does not cover the needs of rapid increase of stiffness, and its endurance behavior is limited, because of the alternating actions to which the elastomer forming the support element is subjected.
A second embodiment of a variable-flexibility support element consists in placing, within the elastomer support element, a rigid insert, for example made of aluminum or plastic. The insert may, like the surface in contact with the spring, comprise notches, which makes it possible to obtain a greater maximal stiffness while increasing endurance behavior. A risk of performance deterioration over time however remains, because of the creep of the elastomer forming the support element.